A. Field of the Invention
This invention relates to a melt spinning process for producing a multifilament yarn of a modified nylon 66 (polyhexamethylene adipamide) having a denier per filament of at least 18, whereby a latent bulk of at least 18% is imparted to the yarn without the application of any special bulking equipment or steps, that is, the yarn is "self-crimping".
D. Description of the Prior Art
In conventional spin-draw processes for producing a nylon 66 multifilament yarn, molten fiber-forming nylon 66 is extruded through spinneret orifices at a given rate to form molten streams. The molten streams cool and elongate in a cooling zone as they move away from the spinneret. The cooling is normally assisted by a transverse stream of flowing air in a quenching chamber, commonly referred to as a chimney, positioned immediately below the spinneret through which the molten streams pass. The molten streams solidify in the lower region of the chimney to form filaments. Conventionally, the filaments are withdrawn from the cooling zone by passing the filaments around at least one rotatable roll, such as a feed roll (driven at a given peripheral speed) and its associated separator roll. The filaments make at least a partial wrap and preferably several wraps around the roll(s) to assure that substantially no slippage of the filaments occur on the roll(s). The extrusion rate and the peripheral speed of the rotatable roll(s) (e.g. feed roll and its associated separator roll) are correlated to provide a yarn having a given denier per filament (dpf). From the feed roll the filaments are normally wound onto a take-up bobbin. The peripheral speed of the take-up bobbin is usually slightly higher than that of the feed roll so as to facilitate winding of the filaments on the bobbin. In practice, a spin finish is usually applied to the filaments just prior to the feed roll, such as, by passing the filaments into contact with a rotatable finish roll which is partially immersed in a finish contained within a resevoir. The filaments converge on the finish roll or in the absence of such on the feed roll to provide a yarn.
It is generally recognized that for carpet yarn applications a yarn bulk of at least about 18% (as hereinafter defined) is required. Applicants have found that when 10 dpf nylon 66 yarn is prepared by the foregoing spin-draw process utilizing a feed roll peripheral speed of about 4800 yards per minute (ypm), a latent bulk of about 18% is imparted to the yarn at a constant dpf, yarn bulk normally increases feed roll peripheral speeds. Unfortunately, in preparing 20 dpf yarns, the peripheral speed of the feed roll is limited to a maximum speed of about 2400 ypm, at which speed the maximum latent bulk imparted to the yarn is only about 15%. In the case of 20 dpf yarn, when the extrusion rate and feed roll peripheral speed are increased sufficiently to impart a latent bulk of 18% or higher to the yarn the filaments stick to one another in the chimney and/or at their point of convergence (e.g. finish roll). Such sticking occurs when the filaments are at a temperature above their stick temperature and ultimately leads to broken and/or damaged filaments and yarn of inferior or unacceptable quality. It will be appreciated that increasing the dpf also results in an increase in the surface area and cross-sectional area of the filaments. Consequently more cooling is needed to reduce the temperature of the filaments to a temperature below their stick temperature. At the same time, as the extrusion rate and peripheral speed of the feed roll are increased, the residence time of the filament in the quenching chamber is reduced.
An object of the present invention is to provide a means for imparting a latent bulk of at least 18% to large dpf nylon 66 yarns utilizing the spin-draw process hereinabove described.
Another object of the invention is to produce the yarn described in the preceeding paragraph without utilizing additional equipment and/or processing steps.
Other objects and advantages of the invention will become apparent from the following detailed description thereof.